Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
  • B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
  • B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
  • B29C55/16—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial simultaneously
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
  • B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
  • B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
  • B29C55/16—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial simultaneously
  • B29C55/165—Apparatus therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould

Definitions

• the present invention is directed to the preparation of biaxially oriented thermoplastic films.
• the present invention pertains to a biaxially oriented thermoplastic film, such as polyethylene terephthalate or polyethylene naphthalate, prepared by simultaneous biaxial stretching in a tenter frame stretcher, wherein the film is simultaneously stretched in both the machine and cross-machine directions while the two beaded edges of the film are held by gripping devices propelled along tracks.
• a biaxially oriented thermoplastic film such as polyethylene terephthalate or polyethylene naphthalate
• thermoplastic polymers such as polyethylene terephthalate or polyethylene naphthalate
• a film transfer and winding section typically includes slitting knives for removing the edges and for dividing the film into more than one final sheet width and finally equipment for winding the sheet into rolls.
• Suitable types of biaxial stretchers include sequential stretchers containing at least two stretching sections for imparting orientation first in one direction (machine or cross-machine) and then in the other direction.
• Sequential stretchers typically impart machine direction orientation first by passing the film over rollers rotating at increasing speeds and then impart cross-machine orientation by means of a tenter frame stretcher. The film edges are gripped by moving tenter clips driven forward at constant speed on tracks which diverge to provide cross- machine direction orientation.
• the stretcher can be a simultaneous biaxial stretcher which performs both machine direction and cross-machine direction orientation in a single step by gripping the edges of the as-cast film with tenter clips on tracks which diverge to impart cross-machine orientation, while the clips are driven forward at increasing speeds to impart machine direction orientation.
• the clip driving means used in the stretching section may be a mechanical device such as a large screw with pitch variably increasing along the clip path, such as described in U.S. Patent No. 3,150,433 to Meeting, or linear electrical motors arranged to accelerate the clips as they advance through the stretching section, such as described in U.S. Patent No. 5,051,225 to Hommes et al.
• the temperature of the film to be stretched must first be adjusted to within a suitable orientation temperature range characteristic of the specific polymer. This is usually accomplished by passing the as-cast film through a preheating zone after the film edges have been gripped by the tenter clips with the clips moving at essentially constant speed and with the clip paths essentially parallel so that no stretching occurs.
• the film may be heated by any of the methods known in the art, usually either by impingement of hot air onto the film and/or by application of radiant heat from electrical heaters of various types. Preheating of the film is then followed by simultaneous stretching in which the paths of the tenter clips gripping the film edges diverge to impart cross- machine direction orientation, while the clips are simultaneously accelerated to impart machine direction orientation.
• the film temperature may optionally be adjusted during stretching by further application of air of controlled temperature or of radiant energy.
• U.S. Patent No. 5,429,785 to Jolliffe A typical example of such a method is described in U.S. Patent No. 5,429,785 to Jolliffe.
• a method is provided for making an ultra-thin, simultaneously biaxially stretched polymer film in a tenter frame by heating the film to the film orientation temperature in the tenter frame prior to stretching and maintaining the film within the film orientation temperature range using radiant heaters while simultaneously stretching the film in the tenter frame.
• the biaxially stretched film of the Jolliffe patent has a gauge uniformity suitable for commercial application with a thickness variation of typically less than 25%, thereby providing improved runnability and ready formation of smooth finished rolls.
• Bead edges are initially created as the film is cast. Normally the bead edges are somewhat thicker than the central film sheet.
• the beads act as cables attached to the edges of the film, providing cross-machine tension to the film between the tenter clips as the clips separate during the machine direction stretching.
• the beads propel the passive (idler) clips and the beads themselves are stretched primarily in the machine direction, since no gripping exists between the clips to apply cross-machine force to the beads.
• the beads may frequently break as they are elongated in the machine direction.
• the bead breaks propagate into the main sheet of the film interrupting the continuous operation needed to produce long rolls of stretched film required for commercial operation.
• the beads and the film can break continuously and emerge from the tenter frame in pieces generally less than a meter in length.
• the heating method applied to the main portion of the film does not reliably heat the bead edges of the film to the proper temperature for orientation, especially when the bead edges are of a thickness appropriate for simultaneous biaxial stretching.
• the beads are usually much thicker than the film and therefore require greater heat input per unit area to reach the desired temperature.
• the beads also commonly receive even less heat input per unit area than the film because they are located at the edges of the heating equipment where they are partially shielded from the radiant heat source if the film is radiantly heated, or may receive less flow of hot air than the central film sheet if the film is heated by hot air. For these reasons the beads usually are considerably cooler than the film. In one instance, radiant heat raised the film temperature by 76°C, and the beads by only 3°C, in the absence of separate bead heating, in a preheating zone.
• the tenter clips are driven by linear electric motors. It has been found that it is not necessary for the linear motors to propel all of the clips. It is more economical to drive only, for example, every third clip, the intervening two clips being propelled by engagement with the film beads. Beads of appropriate thickness are required to sustain the stretching forces and propel the passive clips. It has been found with the present process that a cast bead edge thickness of from 400 to 1000 microns, preferably from 600 to 800 microns, is preferred for a cast PET or PEN film having a thickness of less than 250 microns. If the beads are not the proper thickness or are not maintained in the appropriate temperature range to propel the passive, non-driven clips the beads may break.
• the present invention provides a process for simultaneous biaxial stretching of a thermoplastic film containing beaded edges in a tenter frame wherein the temperatures of the bead edges of the film before and during stretching are raised to temperatures suitable for stretching, which avoids bead breaks which propagate into the film and interrupt the stretching process, minimizes the irregularities along the edges which result from unnecessarily high bead temperatures and enhances the reliability of gripping of the bead edges of the film by the tenter clips.
• the present invention relates to a process for preparing a simultaneous biaxially stretched thermo-plastic film by casting a molten melt of thermoplastic polymer and cooling the polymer to form a film having beaded edges, gripping the beaded edges of the film with tenter clips and directing heat onto the film to heat the film to an orientation temperature range prior to stretching the film simultaneously in both the machine and cross-machine directions, wherein the improvement comprises increasing the temperature of the beaded edges of the film to within the film orientation temperature range prior to or during simultaneous stretching by focusing heat on the beaded edges of the film.
• the present invention relates to a process for preparing a thin, biaxially stretched thermoplastic film comprising the steps of
• thermoplastic film (d) heating the film to an orientation temperature in the tenter frame prior to stretching; and (e) simultaneously stretching the film biaxially to form a biaxially stretched thermoplastic film, wherein the temperature of the beaded edges of the film is increased to within the film orientation temperature range prior to or during simultaneous stretching by focusing heat on the beaded edges of the film using focused radiant heat from electrical heaters or focused hot air impingement from nozzles.
• the focus of heat on the beaded edges of the film is considered not to affect the temperature of the central portion of the film.
• Thermoplastic films and particularly polyester films, such as polyethylene terephthalate and polyethylene naphthalate, having a final thickness after stretching, ranging at least from 0.2 microns to 350 microns may be stretched using this process.
• the films are stretched at least 2 times, and preferably from 2 to 5 times, their original length in the machine direction, and at least 2 times, and preferably from 2 to 5 times, their original width in the cross- machine direction.
• FIG. 1 is a schematic top plan view of the tenter frame used to simultaneously biaxially stretch a thermo-plastic film and illustrates the locations of the various bead heaters used according to the invention. DETAILED DESCRIPTION OF THE INVENTION
• the present invention relates to a process for preparing a biaxially oriented polymer film having beaded edges, which are generally thicker than the central portion of the film, and simultaneous biaxially stretching the film in a tenter frame, while increasing the temperature of the beaded edges of the film to within the film orientation temperature range before or during simultaneous biaxial stretching.
• Heat can be applied selectively to the bead edges at any or all of the following stages of the process:
• non-contact bead heating during the simultaneous stretching process and (4) non-contact bead heating prior to and during film processing steps downstream from the simultaneous stretcher, including further machine direction stretching to increase the strength of the film.
• the choice of bead heating methods is not critical to the invention.
• the bead heating equipment must be capable of focusing heat toward the bead edges of the film with minimal or substantially no effect on the temperature of the central portion of the film, which is preferably controlled by separate means. Independent control of bead temperature is preferable so that bead temperatures can be adjusted for process reliability without affecting the temperature of the main central portion of the film.
• Non-contact bead heating may be performed using hot air impingement by nozzles configured to direct a narrow stream of air along the bead and by radiant heating using electrical heaters.
• Electrical heaters include (1) flat narrow sheathed heaters mounted above or below the bead edges of the as-cast film and located before the tenter clip gripping point; (2) high intensity tubular radiant heaters with parabolic cylindrical reflectors mounted above or below the film and focused at the bead edges located after the tenter clip gripping point and before stretching begins; and (3) tubular sheathed heaters mounted parallel to the tenter clip paths above the film and close to the clips to maximize the heat input to the beads.
• Both hot air and radiant heaters can be used in the film preheat zone upstream from the simultaneous stretcher, within the simultaneous stretcher and in subsequent stretching operations and provide highly oriented films.
• the temperature of the beads prefferably be approximately equal to, or higher than, the temperature of the central film web.
• the film needs to be within an orientation temperature range suitable for the particular polymer.
• the beads acting as carriers for the film may be within or above the film orientation temperature range.
• the need for separate control of bead temperatures is driven both by the unequal heating applied to the beads compared to the film in typical stretcher heating zones, and by the need to separately optimize film and bead temperatures.
• Suitable thermoplastic polymers include but are not limited to amorphous non-crystalline polymers such as polystyrene and polyacrylates as well as crystallizable polymers including polyolefins, polyamides, and polyesters. Preferred are crystallizable polyesters containing as the major acid component an aromatic dicarboxylic acid (or the lower alkyl ester thereof) and as the major glycol component an alkylene glycol.
• aromatic dicarboxylic acid examples include but are not limited to terephthalic acid, isophthalic acid, naphthalene- dicarboxylic acid, diphenoxyethanedi-carboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfodicarboxylic acid and diphenylketonedicarboxylic acid. Most preferred are terephthalic acid or naphthalenedicarbox lic acid.
• the preferred alkylene glycol is ethylene glycol.
• Suitable copolymerizable components which may be added to optimize properties of the desired films, as is well known in the art, include diols such as diethylene glycol, propylene glycol or neopentylglycol; aromatic diacid components such as phthalic acid and isophthalic acid; and aliphatic diacid components such as sebacic acid and adipic acid.
• diols such as diethylene glycol, propylene glycol or neopentylglycol
• aromatic diacid components such as phthalic acid and isophthalic acid
• aliphatic diacid components such as sebacic acid and adipic acid.
• PET polyethylene terephthalate
• PEN polyethylene-2,6-naphthalate
• the process is also applicable to polyester copolymers of PET and PEN, copolymers comprising more that 70% by weight of either PET or PEN, and polymer blends formed by combination of suitable polymers providing that the blend exhibits orientation characteristics typical of PET and PEN during the film forming process.
• FIG. 1 shows a tenter frame stretcher 11 generally suitable for simultaneous biaxial stretching of a thermoplastic film, such as polyethylene terephthalate film or polyethylene naphthalate film.
• a thermoplastic film such as polyethylene terephthalate film or polyethylene naphthalate film.
• a molten polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) polymer is typically melt-extruded through a slit orifice of a die and cast onto the quenching surface of an internally cooled, rotating quench drum held at a temperature of typically 30°C to produce a substantially amorphous self-supporting film W.
• PET polyethylene terephthalate
• PEN polyethylene naphthalate
• the film W is stripped from the drum and moved over heated rollers into a pre-heating section 16 in tenter frame 11 where it is gripped 15 on both sides by tenter clips and heated to an orientation temperature prior to stretching.
• a source of heated air or radiant heat 17 is used to pre-heat the film.
• the orientation temperature range for polyethylene terephthalate (PET) is typically from 80° to 120°C and the orientation temperature range for polyethylene naphthalate (PEN) is typically from 115° to 165°C.
• the orientation temperature range as referred to herein is the temperature range in which molecular orientation of a polymeric film may be effected. Below the orientation temperature range the film tends to break. Above the orientation temperature range the film elongates without orienting.
• the specific orientation range for a given thermoplastic polymer can be readily determined by one skilled in the art.
• the film W is then moved into stretching section 18 where it is simultaneously biaxially stretched in the machine and cross-machine directions while the temperature is maintained within the orientation temperature range of the particular polymer using radiant or air heaters 19.
• the film is stretched at least two times its original dimensions in each direction.
• These steps may include further stretching primarily in the machine direction and heat setting by elevating the temperature in order to dimensionally stabilize the film, or combinations of any of these steps.
• the stretched film F is disengaged 22 from the tenter clips, the edges are trimmed off and the central film is wound into a roll.
• Example 1 A linear motor tenter frame stretcher of the type described in U.S. Patent No. 5,051,225 to Hommes was used to simultaneously biaxial stretch a polyethylene terephthalate film and the teachings of this patent are incorporated herein by reference. The only modifications required were the addition and use of radiant heaters to maintain the film at appropriate temperatures for heating, stretching and heat setting, and the addition and use of bead heaters in the tenter frame to maintain the temperature of the bead edges at the proper operational temperatures in the preheating and stretching sections of the tenter frame as previously described above.
• thermoplastic film was formed by extruding a molten polyethylene terephthalate (PET) polymer from a film forming die onto the surface of a rotating, water-cooled quench drum where it was cooled to produce a substantially amorphous self-supporting film.
• PET polyethylene terephthalate
• the cast amorphous film was 40 cm wide, 180 microns thick across its central main portion and 700 microns thick at each bead edge. The edge thickness tapered from the 700 microns edges to the 180 microns thick central sheet over a span of 4 cm.
• the film was cast at 20 meters a minute.
• the die was of conventional design, with appropriate means to allow adjustment of the cast film profile by adjusting the die lip opening at a plurality of points along the lip.
• a nominal opening of 1.3 mm was maintained between the die lips to provide a suitable pressure drop consistent with the viscosity of the polymer and the flow rate.
• the cast film was then stripped from the quench drum and transported to the entrance of the tenter frame 11 over heated rollers maintained at 80°C to raise the film and bead temperatures but avoid sticking of the film and beads to the rollers.
• the beaded edges of the film were gripped 15 by tenter clips that were initially open and then closed after the bead edges were introduced into the jaws.
• the film entering the clips had a temperature of about 50°C.
• a row of three focused radiant heaters 2 were located on each side of the tenter frame, mounted above the film and aimed outward and downward to focus heat toward the bead edges.
• Each of these heaters consisted of a metal parabolic, cylindrical reflector which was 3.8 cm wide and 28 cm long, with a cylindrical incandescent heating element 25 cm long located at the focus of the parabolic cross-section of the reflector to project nearly parallel rays.
• Each of the heating elements was rated at 2000 watts maximum electrical input, and actual electrical input was made adjustable from zero to 100 percent of this input by a suitable manually adjustable power controller.
• the reflector and heater assemblies were mounted so that the heat rays were projected at angles of 45 degrees to the horizontal toward the film beads.
• the film entered the tenter oven which contained five separate heating zones for preheating 16 the film in preparation for stretching, then stretching the film simultaneously 18 and heat setting 20 (in the last three zones) the stretched film.
• the film was heated by arrays of flat radiant heaters 17, 19 and 21 mounted 35 cm above the film with the heater power inputs adjustable separately for each of the five heating zones.
• the heater elements were Casso solar type C heaters, commercially available and designed to preferentially radiate infrared energy outward from their quartz faces, in this case, downward.
• the clips were moved in approximately straight parallel paths into the preheating section 16 where the film was heated to a temperature of 94°C.
• the paths of the clips diverged and opposed pairs of clips were accelerated causing them to separate from adjacent pairs to simultaneously stretch 18 the heated film in the machine and cross-machine directions.
• the film was stretched 3.55 times its original length in the machine direction and 3.55 its original width in the cross-machine direction.
• the tenter clip paths became approximately parallel again, and the film was heat set by heating it in heat setting zone 20 at a temperature of 200°C where no further stretching occurred. Heat setting reduces dimensional changes when the film is later reheated, as occurs in subsequent processing or in some end uses.
• the film was released 22 from the tenter clips and passed through bead removal knives to a winder which wound the film into rolls.
• the film temperature required for uniform stretching and to develop the desired physical properties was controlled by adjusting the power inputs to the infrared film heaters in the preheat zone 16 and in the stretching zone 18 to obtain the desired film temperatures as measured by Ircon infrared pyrometers which viewed the film on the machine centerline at the end of each of the oven heating zones.
• the following process conditions reliably produced a PET film having consistent physical properties in satisfactorily long roll lengths: Process Condition casting speed 20 meters/minute stretch ratio, each direction 3.55 stretching temperature 94°C heat setting temperature 200°C radiant bead heater power 4900 watts inputs, total for each bead
• the focused radiant bead heaters 2 provided the necessary increase in bead temperature to obtain freedom from film breaks. Greater power input to the heaters caused undesirable thinning of the film inside the beads due to the spreading of radiant heat onto the film.
• Example 2 The linear motor tenter frame stretcher described in Example 1 was used to stretch a polyethylene terephthalate (PET) film having an initial thickness of 2.5 mm and having a final stretched thickness of 350 microns. The thicknesses are around the normal upper limit of thickness for oriented polyester films.
• PET polyethylene terephthalate
• the pre-clip closer bead heaters 1 successfully assured gripping of the thick film beads. Without them the thick films slipped out of the clips and the stretching process failed.
• Example 3 The linear motor tenter frame stretcher described in Example 1 was used to make a highly tensilized polyethylene terephthalate (PET) film having unusually high strength in the machine direction.
• PET polyethylene terephthalate
• the high strength was imparted by first casting and stretching the film simultaneously at conditions similar to those described in Example 1, then stretching further in the machine direction.
• the continued stretching in the machine direction was obtained by adjusting the controls of the linear electric motors to continue accelerating the tenter clips after completion of the simultaneous stretching.
• This example utilized the focused radiant heaters 2 as described in Example 1.
• hot air nozzles 4, 5 and 6 were located at the boundaries between the heating zones at the start of the simultaneous stretch zone and at the start of the next two zones after the initial stretch zone.
• the nozzles were mounted to direct air toward the bead edges of the film and were supplied with heated air from conventional air heaters and fans with separate controls for air temperatures and fan speeds for all six nozzles.
• the supplied air temperature was between 180° and 190°C.
• the beads themselves were not accessible for temperature measurement.
• the maximum machine direction film strength attainable both with and without the added hot air nozzles was determined by measurement of the values of F5, i.e. the stress in a tensile test specimen measured at 5% elongation in a conventional tensile tester.
• MDX machine direction stretch ratio
• Example 4 The linear motor tenter frame stretcher described in U. S . 5 ,051 ,225 to
• Hommes et al was used to make an oriented polyethylene naphthalate (PEN) film.
• PEN polyethylene naphthalate
• thermoplastic film was formed by extruding a molten PEN polymer onto the surface of a rotating, cooled quench drum and cooled to produce an amorphous self-supporting film.
• the film was 51 cm wide, 44 microns thick across its central main portion and 700 microns thick at each bead edge with the edge thickness tapered from the 700 microns edges to the 44 microns central sheet over a span of 4 cm.
• the linear speed of the cast film was 18 meters a minute. Referring to FIG. 1, the cast film was then stripped from the quench drum and transported over heated rollers at 94°C to the entrance of simultaneous biaxial tenter frame 11 where the beaded edges were gripped 15 by tenter clips.
• sheathed electrical heaters 1 which were 25 cm long, 4 cm wide and located 12 mm above and below the film path.
• the electrical power input to the bead heaters 1 was 500 watts to each heater providing a total of 1000 watts for each of the two beads.
• three focused radiant heaters 2 were located on each side of the tenter frame.
• the electrical power input to the focused heaters was 2000 watts to each heater providing a total of 6000 watts for each of the two beads.
• the film entered the tenter oven which was divided into five heating zones for preheating 16 the film in preparation for stretching, stretching 18 the film simultaneously and then heat-setting 20 the film in the last three zones.
• the film was heated by arrays of flat radiant heaters 17, 19 and 21 mounted 35 cm above the film with the heater power inputs adjustable separately for each of the five heat zones.
• the heater elements were commercial Casso solar type C heaters radiating infrared energy downward from their quartz faces. In the preheat zone 16, the film heater 17 raised the film temperature to
• Tubular, sheathed bead heaters 3 were mounted parallel to the paths of the beads, above the film plane, and as close as practical to both the film plane and the edges of the tenter clips in order to radiate as large a fraction of energy into the beads as possible. These bead heaters 3 were 109 cm long, 0.95 cm in diameter, and had power ratings of 5400 watts for each bead. The power inputs to the heaters on the two edges of the tenter were separately adjustable.
• the film After passing through the preheat zone 16, the film was stretched biaxially and simultaneously in stretching zone 18, at a stretch ratio of 3.3 times in both the machine and cross-machine direction.
• the film temperature after stretching was 130°C as measured using a Ircon infrared pyrometer.
• the film passed through heat setting zone 20 (including three separate heated zones), where no further stretching occurred, and where the film temperature was 160°C, 208°C and 133°C in the three zones, respectively.
• the tenter clips on each side of the tenter frame were forced open 22.
• PEN films were made by adjusting the various heat inputs to the film and the beads with the preheat zone tubular bead heaters 3 first turned off. The temperature of the beads was measured. Then the preheat zone tubular heaters 3 were turned on and their power inputs were adjusted for best appearance of the beads of the stretched film at the tenter exit and best idler clip spacing. The bead temperature measurements were repeated.
• Table I summarizes the bead heating conditions and bead temperatures as measured using an Agema Thermovision thermal imaging camera manufactured by Agema Infrared Systems AB, Sweden. The results give the frequency of film breaks for each set of conditions, the observed difference in idler clip spacing associated with the corresponding bead temperature and the appearance of the stretched bead.
• Preheat zone bead heater 3 power input 0 1080 watts 1890 watts

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• 1996
  • 1996-12-11 US US08/763,819 patent/US5753172A/en not_active Expired - Lifetime
• 1997
  • 1997-12-10 EP EP97953124A patent/EP0944468B1/de not_active Expired - Lifetime
  • 1997-12-10 WO PCT/US1997/022599 patent/WO1998025754A1/en active IP Right Grant
  • 1997-12-10 KR KR1019990705170A patent/KR20000057493A/ko not_active Application Discontinuation
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  • 1997-12-10 JP JP52691698A patent/JP4278713B2/ja not_active Expired - Fee Related
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